The Behavior of Flexible MIL-53(Al) upon CH₄and CO₂Adsorption

Abstract

The use of the osmotic thermodynamic model, combined with a series of methane and carbon dioxide gas adsorption experiments at various temperatures, has allowed to shed some new light on the fascinating phase behavior of flexible MIL-53(Al) metal-organic frameworks. A generic temperature-loading phase diagram has been derived; it is shown that the breathing effect in MIL-53 is a very general phenomenon, which should be observed in a limited temperature range regardless of the guest molecule. In addition, the previously proposed stress model for the structural transitions of MIL-53 is shown to be transferable from xenon to methane adsorption. The stress model also provides a theoretical framework for understanding the existence of lp/np phase mixtures at pressures close to the breathing transition pressure, without having to invoke an inhomogeneous distribution of the adsorbate in the porous sample.

Activated MIL-53(Al) for Efficient Adsorption of Dichloromethane and Trichlormethane

“…The MIL-53(Al) samples were prepared following the synthetic approach reported in previous studies (Serre et al, 2007;Boutin et al, 2010).…”

“…A major problem for developing efficient synthesis techniques is to optimize the activation method. Calcination in high temperature (HT) and solvent exchange (SE) are frequently-used activation methods for MOFs (Serre et al, 2007;Boutin et al, 2010). In HT method, the AS samples are put in shallow beds and heated in a muffle furnace at 573-623 K for about three days to remove residues from the pores.…”

Preparation of novel metal-organic frameworks for selective gas adsorption

“…In gas adsorption (such as Xe, CH 4 or CO 2 ), the lp phase transforms into the np phase at low vapor pressures, and the reverse transformation occurs at higher pressures (Figure 2.9). 183 As the affinity of any adsorbate for the closed np form of the framework is always higher than for the open lp structure, the breathing effect in MIL-53 was predicted in a limited temperature range (150-350 K) regardless of the type of guest molecules. …”

“…133,[172][173][174][175][176][177][178][179][180][181][182] Scheme 2.2 Classification of dynamic porous coordination polymers [133][134] Figure 2.9 (Left) The transformation of lp and np structures in MIL-53(Al) during gas adsorption; (Right) Temperature-Loading Phase Diagrams for Xe, CH 4 and CO 2 adsorption (P max and T max are the pressure and temperature above which no breathing transition takes place for a given guest molecule.) 183 As typical flexible MOFs, MIL-53(Al or Cr) has attracted a lot of attention, due to the occurrence of structure transformation (large-pore phase, lp and the narrow-pore phase, np). 178,[183][184][185][186][187][188] At room temperature and upon the removal of guest molecules, the lp phase is the most stable form.…”

“…183 As typical flexible MOFs, MIL-53(Al or Cr) has attracted a lot of attention, due to the occurrence of structure transformation (large-pore phase, lp and the narrow-pore phase, np). 178,[183][184][185][186][187][188] At room temperature and upon the removal of guest molecules, the lp phase is the most stable form. In gas adsorption (such as Xe, CH 4 or CO 2 ), the lp phase transforms into the np phase at low vapor pressures, and the reverse transformation occurs at higher pressures (Figure 2.9).…”